Isoflurane, 1-chloro-2,2,2-trifluoroethyl difluoromethyl ether (CF.sub.3 --CHCl--O--CF.sub.2 H), has been the most widely used inhalation anesthetic over the past decade. Isoflurane, its preparation and use, are disclosed in Terrell U.S. Pat. Nos. 3,535,388 and 3,535,425, both issued on Oct. 20, 1970.
A number of preparations of isoflurane have been published. In one synthesis, isoflurane is prepared by the chlorination of 2,2,2-trifluoro-ethyl-difluoromethyl ether (CF.sub.3 --CH.sub.2 --O--CF.sub.2 H). In order to prevent the level of the impurities CF.sub.3 --CCl.sub.2 --O--CF.sub.2 H, CF.sub.3 --CH.sub.2 --O--CF.sub.2 Cl and CF.sub.3 --CHCl--O--CF.sub.2 Cl in the reaction mixture from exceeding acceptable levels, i.e. about 10% by weight, the chlorination must be terminated when only about 60% of the starting material, CF.sub.3 --CH.sub.2 --O--CF.sub.2 H, has been consumed. Continued chlorination will produce excessive amounts of the by-product 1,1-dichloro-2,2,2-trifluoroethyl difluoromethyl ether, (CF.sub.3 --CCl--O--CF.sub.2 H).
In the above-described synthesis, after termination of chlorination, the reaction mixture comprising isoflurane, the starting material, and the above-mentioned impurities is subjected to fractional distillation. The starting material, CF.sub.3 --CH.sub.2 --O--CF.sub.2 H and CF.sub.3 --CH.sub.2 --O--CF.sub.2 Cl, recovered thereby, are recycled to the chlorination stage.
Heretofore, CF.sub.3 --CCl.sub.2 --O--CF.sub.2 H recovered by the fractional distillation, has been reduced to form isoflurane by a method utilizing metallic zinc and aqueous acetic acid, which is expensive, both in terms of time and equipment. The zinc method has a further disadvantage in that it poses an environment disposal problem due to the formation of Zn(OCOCH.sub.3).sub.2 and CH.sub.3 --O--CF.sub.2 --CHCl--O--CF.sub.2 H.
In accordance with the present invention, the foregoing process is substantially improved in terms of efficiency, cost and environmental disposal problems.